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Most cases of monkeypox post-vaccination occurred within 2 weeks of the first Jynneos dose, a single-center study found, but some breakthrough cases developed weeks after a second dose of the vaccine.

Of 90 individuals who tested positive for monkeypox after a single dose of Jynneos at a large monkeypox testing and vaccination site, 77% of the cases occurred within 14 days of the first dose and 14% within 14-28 days of the first dose, reported Aniruddha Hazra, MD, of Howard Brown Health in Chicago, and colleagues.

In the eight cases occurring 28 days after vaccine initiation, five positive tests came back following a second dose of the modified vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine.

"Of concern is that at least two breakthrough infections were observed in individuals at least 3 weeks after a second dose," wrote Hazra and colleagues in a research letter.

MVA-BN, the Jynneos vaccine, is approved for the prevention of monkeypox disease in adults, and individuals are considered fully vaccinated 14 days after receiving the second dose.

"Early immunogenicity data around MVA-BN shows good immune response with a single dose," Hazra told 番茄社区app. "Prior to moving to intradermal dosing, the public health strategy was to maximize first doses and hold off on second doses due to limited vaccine supply. We wanted to see how this approach may translate in the real world based on our experience."

In their paper, the researchers noted that "because the incubation period for monkeypox is 3 to 17 days, some of the cases occurring between 1 and 14 days after vaccination may not represent true vaccine failure," as "patients may have sought vaccination after realizing they were exposed."

Preliminary data from the CDC reported last week suggested that at-risk individuals were 14 times less likely to be infected with monkeypox at least 2 weeks after the first dose of Jynneos when compared to individuals who were eligible but didn't receive the vaccine.

During a call with reporters last week hosted by the Infectious Diseases Society of America, members of the White House Monkeypox response team urged eligible individuals to follow up to get maximally protected.

Borrowing from a "Star Trek" reference, the team's deputy coordinator Demetre Daskalakis, MD, MPH, asked: "Why would you have your force field at level five if you can have it at level 10 against the threat?"

Carl Dieffenbach, PhD, director of the Division of AIDS at the National Institute of Allergy and Infectious Diseases, agreed and continued the reference.

"What we have seen in the past is that if you don't get the second shot, the force field drops to zero," said Dieffenbach. "When you get a booster, you have sustained antibody response. It's an important piece of advice; I don't want people to get complacent. We do not want people to lose their force field by skipping the second shot."

The study from Hazra's group involved 7,339 individuals who were vaccinated with Jynneos at Howard Brown Health in Chicago, with 400 testing positive for monkeypox infection. Overall, 90 cases occurred at least 1 day following vaccination (median 8.5 days), including 37 cases in the 1-7 days after the first dose, 32 cases in the 8-14 days after, 13 in the 15-28 days after, and the eight cases 28 days after the initial dose.

People with HIV comprised 37% of the cases, of whom 73% were virologically suppressed (25 of 34 individuals).

Of the eight patients testing positive for monkeypox 28 days after the first dose, four had HIV, virologically suppressed in all four cases. Most of these patients had fewer than 10 lesions, and systemic symptoms included fevers, chills, myalgia, headache, fatigue, and lymphadenopathy. Three patients also had other co-infections (rectal gonorrhea, oropharyngeal gonorrhea, and rectal chlamydia).

The researchers acknowledged various limitations to the data, including that they did not include risk factors, nor did it include information on the date of monkeypox exposure. Additionally, the data were limited by the lack of uniform post-vaccination data.

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